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QLDPhysics2025

QCE Physics 2025

Walkthrough of the 2025 QCE physics exam: what it assessed, strategy tips, and the common errors flagged in the official marker report.

Marks
97
Time
180 min
Authority
QCAA
Updated
Open the official PDF Official marking notes
Key fact

This paper was set on the 2019 QCAA syllabus. From the 2026 external assessments the 2025 syllabus applies, so some content and the exam format have changed. It is still useful practice, but check the current QCAA Physics syllabus and QCAA's 2026 key changes before relying on it. The mark and timing figures at the top of this page are a guide based on the 2024 papers (two papers, each with 90 minutes of working time), not QCAA's official structure for every year. Marks and question types vary, so use QCAA's own paper.

What this paper assessed

The QCAA Physics external assessment is the final 50% summative external, covering Units 3 and 4 of the senior syllabus:

  • Unit 3 - Gravity and electromagnetism: gravity and motion (projectile and circular motion, gravitational fields and orbits), and electromagnetism (electric and magnetic fields, the motor effect, and electromagnetic induction via Faraday's and Lenz's laws).
  • Unit 4 - Revolutions in modern physics: special relativity (time dilation, length contraction, mass-energy equivalence), and quantum theory and the Standard Model (the photoelectric effect, atomic spectra, and fundamental particles).

You are given the QCAA formula and data book. The paper mixes objective and short-response items, many of which require extracting data from a graph, applying a relationship, and commenting on the limitations of the model. The extended-response items reward structured reasoning, with each equation stated and its variables defined, units carried, and answers given to appropriate significant figures.

Structure and timing

QCAA sets the external assessment as more than one paper, and the number of marks, the sections and the question types differ from year to year. Open the official paper for the exact structure of this year; the marks and time shown at the top of this page are a guide only.

  • Pace by marks. Share your working time in proportion to the marks on offer, so a 6-mark item gets about three times the time of a 2-mark item. Flag any multiple choice item that runs long and return to it.
  • Use perusal time. Scan for the data-heavy items and the longest calculations or extended responses so you can plan them early.
  • Subject habits. Set out every calculation on three lines: the relationship, the substituted values with units, and the final answer with units and appropriate significant figures. For graph-based items, mark the gradient and intercept on the page before stating their physical meaning, and keep a few minutes at the end to check units, vector directions and significant figures.

Worked practice questions (exam-style)

Worked example

Question 1 (5 marks): A satellite orbits Earth in a circular orbit of radius r=7.0×106 mr = 7.0\times10^6\ \text{m}. Given G=6.67×10−11 N m2kg−2G = 6.67\times10^{-11}\ \text{N m}^2\text{kg}^{-2} and Earth's mass M=5.97×1024 kgM = 5.97\times10^{24}\ \text{kg}, find the orbital speed.

For a circular orbit the gravitational force provides the centripetal force:

GMmr2=mv2r.\frac{GMm}{r^2} = \frac{mv^2}{r}.

The satellite mass mm cancels, giving
v=GMr.v = \sqrt{\frac{GM}{r}}.

Substitute:
v=(6.67×10−11)(5.97×1024)7.0×106=3.982×10147.0×106.v = \sqrt{\frac{(6.67\times10^{-11})(5.97\times10^{24})}{7.0\times10^6}} = \sqrt{\frac{3.982\times10^{14}}{7.0\times10^6}}.

v=5.69×107=7.5×103 m s−1.v = \sqrt{5.69\times10^{7}} = 7.5\times10^{3}\ \text{m s}^{-1}.

The orbital speed is about 7.5 km s−17.5\ \text{km s}^{-1}. The key step examiners reward is cancelling mm to show speed is independent of satellite mass.

Worked example

Question 2 (6 marks): A straight conductor of length 0.25 m0.25\ \text{m} carries a current of 3.0 A3.0\ \text{A} at right angles to a uniform magnetic field of 0.40 T0.40\ \text{T}. (a) Calculate the force on the conductor. (b) Explain how this force underlies the operation of a DC motor.

(a) The motor-effect force on a current-carrying conductor is F=BILsin⁡θF = BIL\sin\theta, with θ=90∘\theta = 90^\circ so sin⁡θ=1\sin\theta = 1:

F=(0.40)(3.0)(0.25)=0.30 N.F = (0.40)(3.0)(0.25) = 0.30\ \text{N}.

(b) In a DC motor, current flows through a coil in a magnetic field. Each side of the coil carries current in opposite directions, so by F=BILF = BIL the two sides experience forces in opposite directions, producing a torque (a couple) that rotates the coil. A commutator reverses the current each half-turn so the torque keeps driving the coil in the same rotational sense, sustaining continuous rotation. The mark for the explanation requires linking F=BILF = BIL to the opposing forces producing a turning effect.

Worked example

Question 3 (4 marks): In a photoelectric experiment, light of frequency f=8.0×1014 Hzf = 8.0\times10^{14}\ \text{Hz} ejects electrons from a metal of work function ϕ=3.0×10−19 J\phi = 3.0\times10^{-19}\ \text{J}. Calculate the maximum kinetic energy of the emitted electrons. (h=6.63×10−34 J sh = 6.63\times10^{-34}\ \text{J s}.)

Use Einstein's photoelectric equation, Ek,max⁡=hf−ϕE_{k,\max} = hf - \phi:

hf=(6.63×10−34)(8.0×1014)=5.30×10−19 J.hf = (6.63\times10^{-34})(8.0\times10^{14}) = 5.30\times10^{-19}\ \text{J}.

Ek,max⁡=5.30×10−19−3.0×10−19=2.3×10−19 J.E_{k,\max} = 5.30\times10^{-19} - 3.0\times10^{-19} = 2.3\times10^{-19}\ \text{J}.

So the maximum kinetic energy is about 2.3×10−19 J2.3\times10^{-19}\ \text{J}. Conceptually, this result supports the particle (photon) model of light: each photon delivers a quantised energy hfhf, and only the excess above the work function appears as electron kinetic energy - a fact the wave model cannot explain. Stating that significance earns the reasoning mark.

Common errors students made

The 2025 QCAA marker report flagged missing units, mixing scalar and vector quantities, treating projectile motion as one-dimensional, and forgetting that induced EMF depends on the rate of change of flux rather than the flux itself. Further recurring traps:

  • Numbers without defined variables or stated equations, which forfeits method marks.
  • Not cancelling masses or rearranging cleanly in orbital and field problems, leading to wrong powers of ten.
  • Relativity answers that omit the frame - say which observer measures proper time/length and which measures the dilated/contracted value.
  • Describing the photoelectric effect or spectra without stating the quantum significance of the result.
  • Rounding mid-calculation, which shifts the final significant figures.

How to use this paper

Sit the paper under timed exam conditions, then mark against the official marking guide and marker report using the QCAA links at the top of this page, noting where method marks fall. Rebuild every calculation that lost more than half its marks, writing the named equation and defining each variable before substituting. For graph items, practise reading gradient and intercept and stating their physical meaning. Keep an error log sorted by topic (orbits, motor effect, induction, photoelectric, relativity) and re-test that class next session.

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